FAA Flight Instructor Airplane (FIA)Weather and Weather ServicesEasy
A flight instructor is briefing a student on fog formation along the California coast. Warm, moist air is moving horizontally inland over the cool coastal waters and the adjacent cool land surface, causing the air to be cooled to its dew point. Which type of fog is most likely to form under these conditions?
- ARadiation fog
- BSteam fog
- CAdvection fog
- DUpslope fog
Show answer & explanationAnswer & explanation
Correct answer: C. Advection fog
Advection fog forms when warm, moist air moves horizontally over a colder surface (land or water), cooling the air to its dew point. It is common along coastlines and can occur with wind, unlike radiation fog which requires calm, clear conditions.
Why the other options are wrong
- A. Radiation fog forms from nighttime surface cooling under clear skies and calm winds, not horizontal air movement.
- B. Steam fog forms when cold air moves over much warmer water, the opposite temperature relationship.
- D. Upslope fog forms when moist stable air is forced up rising terrain, not simply moved horizontally.
Advection Fog
Fog that forms when warm, moist air moves horizontally over a colder surface, cooling to its dew point.
- Common along coastlines and in winter over snow-covered ground
- Can form with wind present, unlike radiation fog
- Often more extensive and persistent than radiation fog
Memory trick: Advection = 'A' for Air moving horizontally Across surfaces